BACKGROUND AND DESIGN: A multi-centre, open, prospective study of 12 months duration was performed to assess safety, efficacy and tolerability of topical calcipotriol in the long-term treatment of psoriasis. One hundred and sixty-seven adults with chronic plaque psoriasis who had previously responded to calcipotriol entered the study. Disease activity was monitored using the psoriasis area and severity index (PASI). Calcipotriol ointment 50 micrograms/g was applied twice daily until remission was attained. Treatment was then stopped but reinstituted in the event of relapses. RESULTS: Of the 167 recruited patients, 6 patients did not receive any treatment during the trial. A total of 39 patients were withdrawn: 15 due to inadequate control of their psoriasis, 9 due to irritant reactions, 7 due to defaulting and 8 for miscellaneous voluntary reasons. A further 24 patients either reached the study medication limit of 2,500 g or were considered to have completed the study a few weeks prior to the 12-month period. Accordingly, 98 patients were assessable after 12 months of therapy. Complete clearing was obtained in 26% of subjects, who then used the treatment intermittently. The remaining patients required continuous treatment for 12 months. The mean PASI fell from 8.1 (SD +/- 6.67, n = 167) at baseline to 3.90 (+/- 3.50, 136) at 2 months and 2.71 (+/- 2.12, 98) at 12 months. There was no rise in the mean serum total calcium. CONCLUSION: Calcipotriol ointment was safe, effective and well tolerated.